Method of and means for optically reproducing sound



April 19, 1938. A. A. RADTKE 2,114,939

METHOD OF AND MEANS FOR OPTICALLY REPRODUCING SOUND Filgd Dec. 27. 1922 s SheetQ-Sheet 1 April 19; 1938. A. A. RADTKE 2,114,939

METHOD OF AND MEANS FOR OPTICALLY REPRODUCING SOUND Filed Dec. 2?. 1922 5 Sheets-Sheet 2 April 19, '1938. A. A. RADTKE 2,114,939

METHOD OF AND MEANS FOR,OPTICALLY REPRODUCING SOUND Filed Dec. 27. 1922 3 Sheets-Sheet 5 Patented Apr. 19, 1938 UNITED STATES PATENT OFFICE METHOD OF AND MEANS FOR OPTICALLY REPRODUCING SOUND Application December 2'1, 1922, Serial No. 609,196

83 Claims.

- This invention relates to means for recording and reproducing sounds, especially musical sounds and articulate speech.

The general object of the invention is to devise a method of and provide means for the optical recording and reproduction of sound, through the instrumentality of a traveling photographic strip, such as a motion picture film.

Although I am aware that attempts have heretofore been made to achieve this broad purpose, I seek, by the present invention, to provide an improved optical sound recording and reproducing system which shall be free from the defects of those heretofore proposed, practical and accurate in its action, and which shall be readily capable of commercial application to the production of so called talking motion pictures, to the re cording of speeches, court proceedings, and for other purposes for-which mechanical recording devices are now employed.

The invention contemplates impressing upon a beam of light, by means of a telephone transmitter and an electro-magnetic device, fluctuations or variations corresponding in frequency and intensity to the sounds to be recorded, and projecting this fluctuating or vibrating beam of light upon a traveling sensitized film, so that a photographic record is made. This record is then reconverted into sound by passing it in front of a source of light, so that the resultant fluctuating beam is projected onto a light sensitive device known as a photo-electric cell, the varying currents thus set up corresponding to the pitch and intensity of the original sound. These currents are extremely feeble, however, and it is therefore necessary to increase their strength. This I do by cooperatively connecting the photo-electric cell in circuit with a suitable thermionic amplifier, to which is also connected a telephone receiver or loud talker", in which the sounds are reproduced.

A specific object of the invention is to so arrange the circuit connections of the photo-electric cell and amplifier as to secure a maximum of eiiiciency in reproduction. This so arranged circuit combining a photo-electric cell and amplifier is important not only in sound reproduction but is specifically itself'important and as stated above an object of this invention particularly in that it is capable of transforming high speed light variations through the feeble energy responses of a photo-electric cell into corresponding current impulses of substantial and readily usable values.

Another specific object is to provide an improved type of record, in combination with an improved method of causing its image to act upon the photo-electric cell, whereby the cell is kept constantly energized, and thus rendered still more effective in its reproducing action.

Other objects of the invention will hereinafter appear, as the description proceeds. In order that the invention may be more readily understood, and its nature better comprehended, reference is had to the accompanying illustrative drawings, forming part of this specification, and in which:

Fig. l is a diagrammatic view conventionally showing one arrangement of my improved electro-magnetic optical sound recording apparatus;

Fig. 2 is a similar view showing my improved reproducing apparatus;

Fig. 3 is a front view, on an enlarged scale, showing one form the beam of light may take, and illustrating the manner in which it is used to produce a record on the film;

Fig. 4 is a front elevation, on an enlarged scale, of the photo-electric cell, showing my novel shield attached thereto;

Fig. 5 is a conventional showing of a fragment of the film, having thereon a photographic record of such a nature as might be formed by the spot of light shown in Fig. 3;

Fig. 6 is a diagrammatic view, somewhat similar to liiig l, but showing a slightly diiferent method of producing-the recording beam;

Fig. 7 is a view similar to Fig. 3, but showing the shape of the beam illustrated in Fig. 6; and

Fig. 8 is a view similar to Fig. 5, but illustrating a record of such a nature as might be formed by the spot of light or image shown in Fig. '7.

Referring to the drawings in detail, and more particularly to Fig. 1 thereof, I designates a powerful electro-magnet of the horseshoe type, supplied with current from suitable mains l0, and having a pair of pole pieces 2 and 3. These pole pieces are arranged with their ends in close proximity and are preferably made tapering so as to produce a very intense magnetic field be tween them.

Suspended in any suitable way between the pole pieces 2 and 3 is a bi-filar conductor or looped filament I, preferably having its strands extending parallel with the pole pieces. A telephone transmitter 1 associated with a suitable battery 0, is arranged to receive the sound to be recorded or transmitted, and serves to convert such sounds in the well known way into variable currents, which currents are impressed upon the looped filament 4, either directly, or by means of the usual transformer or induction coil I, 6. In other words, sounds'striking the diaphragm of the transmitter I will cause currents to flow in the filament l proportional in strength and frequency to the intensity and pitch of the sounds.

. According to the well known law, that a current flowing through a conductor in a magnetic field will cause such conductor to move, it is obvious that the' looped filament 4, due to the variable currents which transverse it, will be thrown into a state of vibration, such vibration being synchronized with the vibrations of the sound which strike the diaphragm of the transmitter.

In order to transform the sound waves into their optical equivalents, I propose to impress upon a beam of light, fluctuations corresponding to the vibrations of the filament 4. This may be done by interposing such filament directly in the path of the beam of light so as to intercept it to a greater or less extent, but as shown in the drawings, I produce the desired efiect by mounting a very small and light mirror 9 upon the filament 4, so that the mirror partakes of the vibrations of the filament.

An electric lamp ll of the incandescent type and preferably having a concentrated filament is supplied with current from the mains i0 and is mounted in a housing II which is provided with condensing lenses it of any suitable character. Beyond the lenses I 3, I preferably provide the housing with a projecting funnel shaped tube or nozzle I, having a restricted open end M through which a small beam of light is projected onto the mirror 9, as indicated by the dotted line 2:.

This incident beam is reflected from the mirror 8 in some such direction as indicated by the dotted line 1:, and is caused to fall upon a shield plate ll, having a narrow slit or slot 20 extending across the same. Behind the shield plate is, a photographically sensitized strip or film i5 is caused to travel, such strip or film being of the same nature as that commonly employed for motion pictures. For simplicity of illustration, this strip I! is shown in Fig. l as being carried upon two reels l6 and H, the latter reel being driven by an electric motor l8, supplied with.

current from the mains It. In practice, however, such an elementary arrangement would not, of course, be operative because of the fact that the reel ll would constantly increase in diameter as the film was wound upon it, and would thus cause the film to travel past the slit 20 with an -wheel or the like, independent of the take-up reel.

Referring now to Fig. 3, I have here endeavored to illustrate the general appearance of a spot of light caused by the projection of such a beam in the manner described. It will be seen that this spot of light, which I have designated a, is of relatively great width and'length as compared with the width of the slit 20, so that the larger part of the spot of light falls upon the shield plates II, and only a comparatively small part passes through the narrow slit and impinges upon the sensitized strip or film.

If, new, sounds such as music or articulate speech are produced in front of the transmitter I, themirror 9 will be caused to vibrate in synchronism with the-sound waves, and the spot of light a, in Pig. -3, will be caused to fluctuate or" oscillate laterally from side to side, traveling back-and forth along the slit 2.; when the spot of light stands still in the position shown in Fig. 3, and the film it travels, it is obvious that a photographic record will be made consisting of but a simple band of uniform width, that is to say, of a width equal to that of the beam or spot of light a. When, however, this beam or spot of light is caused to fiuctuate'or vibrate laterally,

of these teeth being proportional to the ampli-,

tude of the vibrations, that is, to the intensity of the sound, and the distance between these teeth being inversely proportional to the frequency of the vibrations, that is, to the pitch of the sound.

Owing to the great difiiculty of properly representing such a record by a line drawing, it is not intended to convey the impression that Fig. 5 depicts an actual photographic record with any substantial degree of accuracy, but it is intended to merely represent in a conventional way the general character of such a record, namely, that it comprises a central band with teeth or projections at opposite sides thereof. While in the drawings it has been necessary to show these teeth as sharply defined, in an actual record they will, of course, be more or less fuzzy, and vague in their form. The size and number of these teeth or projections will, however, correspond actually with the intensity and pitch of the sound being recorded.'

In Fig. 2, I have diagrammatically illustrated an arrangement by means of which a photographic record of the type shown in Fig. 5 may be converted again into sound. Referring to this figure, Ii designates the developed film or record strip, or rather, a positive print from such strip, and it is shown as wound upon the same reels l6 and II, the latter being driven by a motor i8. A suitable lamp II is mounted in a housing l2 having condensing lenses ll arranged in front of an aperture it, through which a concentrated beam of light is projected. The record strip I5 is placed in the path of this beam, and is caused to travel past a slit 2| in a shield plate i9, similar to that described in connection with Fig. 1. That part of the beam of light passing through the record strip and the slit 20 serves to project the image of a n w but ever changing portion of the record upon suitable receiving apparatus.

This receiving apparatus comprises as one of its essential elements, what is known as a photoelectric cell, designated in its entirety by the reference numeral II. This cell which is shown diagrammatically in Fig. 2 and in more detail in Fig. 4, comprises an evacuated glass vessel or bulb having its inner surface coated with a lightresponsive material, such as potassium, as indicated at 22. The inside of the bulb is usually first silvered like a mirror and the potassium coating is then applied thereto. Two electrodes ane sealed into the glass and enter the interior of the bulb, one of these electrodes, designated at 2! in Fig.2, making contact with the sensitive coating of the cell and constituting the oathode, and the other electrode comprising a ring shaped grid, supported at the center of the bulb, as indicated at 24 in Fig. 2. It is not thought to be necessary to devote further space to the discussion of the details of construction or the theory of operation of such a photo-electric cell, as it has now become a well known piece of apparatus. Suflice it to say that when in darkness, the resistance between the cathode 25 and the anode 24 is almost infinite, but this resistance is reduced and the cell rendered conductivein proportion, as light falls upon the active or sensitive material with which the interior of the cell is coated. That is to say, the stronger the illumination of this sensitive coating, the greater the conductivity of the path between the electrodes. Thus, when connected with a suitable battery, and exposed to a fluctuating beam of light, correspondingly varying currents are caused to flow through the cell. Perhaps better expressed-electrons are emitted by the cathode in proportion to the quantity of light striking it and they are attracted to and carried away by the positive anode. This action has no inertia and no lag but has almost no energy value.

In order that light may enter the cell and produce the efiect just described; it is formed with an uncoated area 23 which is substantially transparent, such transparent portion or window being opposite the cathode 25.

The beam of light. projecting the ever varying image of the photographic record on the strip 15', is directed toward the window 2Z1 as indicated by the dotted line 2 in Fig. 2, so that this fluctuating or varying beam may produce corresponding variations in the resistance of the cell.

In Fig. 4, I have endeavored to indicate, by the white area at the center, the appearance of the spot of light caused by the projection of the ever varying image of the photographic record, as the film travels past the slit 20. It will be noted that this image or spot of light comprises a central portion b corresponding to the central band b in Fig. 5, and more or less of a tooth or projection c on each side, corresponding to the teeth or projections c in Fig. 5. As the film travels past the slit, these projections will, of course, vary from instant to instant in length and width, while the central portion 1) of the image remains'practically constant. The variations in the quantity of light thus entering the window of the cell would probably be suflicient to cause it to respond, but Ihave found that the cell works very much more efliectively it this central portion of the image be obliterated and not permitted to act upon the cell. To this end, I place across the window 23 of the cell, a strip or band 23 of opaque material, such strip or band extending parallel with the record film and being of a width equal to or preienbly slightly less than the width of the image b of the central band b of the record. The image of this central band portion thus falls upon the opaque strip 23 and hence is obscured and prevented from entering the cell, the only light passing into the cell .being that due to the teeth or projections c. It is obvious that such an arrangement produces a much more elective operation of the cell because with it the greatest percentage of variation of the light is produced as successive .teeth or projections of the image pass through the window. Without the strip or screen 23, the maximum variation of light would he onlyin the ratio of the area of the entire white spot to the area of the central portion b thereof, while with the strip or screen the maximum variation will be equal to the ratio between the combined area of the teeth 0 and practically zero. Thus, a much greater percentage of variation can be obtained.

There is another important point to be noted, however. I prefer to make the width of the strip 23 slightly less than the width of the. central portion b of the image, so that even at those moments when the image is without teeth or projections c, that is to say, in moments of silence, the cell will never be wholly deenergized but will be maintained in an active condition by reason of the slight leakage of. light past the screen or strip 23, such leakage being due to the slight overlapping of the central portion b of the image beyond the side edges of the screen or strip 23. I have found that the cell responds more readily from a slightly energized condition than from a condition of zero energization.

Referring again to Fig. 2, I propose to combine with the photo-electric cell just described, one or more amplifiers of the thermionic type, one only of such amplifiers being shown in the drawings. The amplifier is designated in its entirety by the reference numeral 29 and comprises the usual grid 23, plate 31 and filament 35, the latter being maintained at a suitable temperature by means of a battery 36 and constitutes the cathode of this thermionic electronic amplifier. The grid 28 of the amplifier is connected directly by a link-means shown in the form of a conductor 21 to the cathode 25of the photo-electric cell. The battery employed in connection with the ampliher and photo-electric cell is of any suitable voltage and is shown as comprising three sections, 3!, 32, and 33. The voltage of the sections 3| and 32 in series are applied to the electrodes of the photo-electric cell, the negative side of the section 3| being connected to a point 26 in the conductor 21 through a high resistance 30, and the positive side of section 32 being connected at 32 by means of a conductor 40 with the anode 24 of the photo-electric cell. The filament 35 of the amplifier is connected by a conductor 34 to the junction point 3|, and a telephone receiving set 39, or other electro-magnetic sound producing means is connected in circuit by means of a conductor 33 with the plate 31 and the positive side of the battery section 33.

It will be particularly noted that the impedance 30, which is shown as a pure ohmic resistance,- must be relatively high and the best results can be obtained when this resistance is of the same order of magnitude as that of the photoelectric cell.

With apparatus arranged as above described and as shown in Fig. 2, it will therefore be apparent that as the fluctuating beam of light or varying image is projected into the photo-electric cell, the conductivity of this cell will be correspondingly varied and a pulsating current will be caused to flow through the cell from the battery sections 3| and 32 over the conductors 40 and 33', including the resistance 30. As the current through this circuit varies, the presence of the resistance 33 will cause the potential at the point 23 to rise and fall in proportion to changes in the value of the current, and this varying potential will be transmitted by the conductor 21 to the grid 33 of the amplifier. Thus, ina well known way, greatly modified currents ar'etset up through the receiver 33, such currents varying in exact synchronism with the current variations in the circuit through the photo-electric cell and consequently in exact synchronlsm with the linetuations in the beam of light projected into such v cell. By this means, the photographic record on the strip or fllm It is recohverted into sound in the receiver 39. Thus, the sound originally impressed upon the transmitter 1 is electro-magnetically and photographically recorded on a sensitized strip, and is then reproduced, with all of its original qualities, by causing a positive print of such record strip to produce a fluctuating beam of light which acts upon a photo-electric cell, thereby setting up feeble variable currents which are then suitably amplified and converted into sound by an electronic amplifier operating electro-magnetic receiver.

,During the development of this invention, I experimented with an incandescent lamp of that type in which the filament consists of a closely woven helix of fine wire. and with such a lamp, I succeeded in producing photographic sound records presenting an appearance quite different from that shown in Fig. 5. In Fig. 6, such a helical filament is shown at 4|. By means of a condensing lens 42 and tube 43, the image of the filament 4| is thrown upon the mirror 9, carried by the 'bi-fllar conductor 4, as indicated at :r. and this image is in turn reflected onto the shield plates I! as indicated at y, the image itself being designated at d.

In Fig. 7, I have endeavored to show an en-* larged detailed view of the appearance of this fragment of the image of the filament ll as it appears when thrown upon the shield plates I! having the slit 20 formed in them. The image (1 comprises a bright zig-zag line having sharp points d, corresponding to the convolutions of the helix of the originalfllament. The slot 20 is preferably of such width as to permit only that portion of the image corresponding to a single convolution to pass through.

I have found that when such an image is vibrated transversely of the record strip, sheet or film by means of the variable currents in the bifilar conductor 4, a record is produced having somewhat the general appearance as that indicated in Fig. 8. This record comprises a central band e of more or less uniform width, similar to the band b in Fig. 5, but on eachside of this band e are a large number of exceedingly fine teeth I. In practice, these teeth are so fine and so close together that they present the appearance of a series of light and dark lines. It is of course, impossible to properly represent this record in an ink drawing, but Fig. 8 is intended to merely indicate its general nature. In an actual record, of course, the central band and the teeth or lines are not sharply defined, but are more or less hazy and merge the one into the other. Moreover, at certain parts of the film, the lines or teeth are crowded much more closely together than at other parts, thus corresponding to sounds of different pitch. In this connection, it will, of course, be understood that the travel of the film or record strip past theslip 20 is relatively slow, as compared with the frequency of vibration of audible sound. The slower the speed of travel of the film, obviously the smaller space a given record will occupy.

From the foregoing, it will be seen'that I have devised a novel and effective method for optically recording and reproducing sound, including articulate speech, audit is thought that the many advantages and useful applications of the invention will be apparent without further discussion.

It is, of course, obvious that the fluctuating beam of light on which the sound vibrations are regard this method as forming part of the present invention.

My continued experience with my combination of photo-electric cell and electronic amplifier in high speed work shows that the photo-electric cell electrode linked to the grid of the amplifier imparts to the grid instantaneous potential changes with only an average but more slowly varying potential being maintained by the impedance 30. This impedance 3! floats the grid 2! and imparts a normal negative bias by battery sectionjl but holds it subject to instantaneous potential changes in proportion to electrons emit ted by photo-electric cathode 22. This impedance It is an electron restorative impedance, electrons flowing under the electric motive force of sources SI and 32. It should be noted that no batteries are located in the link means shown as conductors 2|, 2 and 21. were any included in this highly sensitive connection the capacity coupling to ground and the large parts (batteries) connected with cathode 35 would shunt out nearly all high frequency potential variations. The grid 2! and its activating photo-electric cell electrode must freely iioat for faithful operation of the amplifier.

Although I have shown much only in diagram I contemplate the use of the best instrumentalities known to the art for moving film without change in speed,' producing steady light and supplying electric potentials. I have shown and described how to use them for good results.

What I claim is:

1. Means for converting a fluctuating beam of light into sound, comprising a photo-electric cell on to which the beam is projected, a telephone receiver, a source of current, and an electronic amplifier. operatively connected with said cell, source of current, and receiver.

2. Means for converting a fluctuating beam of light into sound, comprising a photo-electric cell on to which the beam is projected, said cell having a pair of electrodes, a current source having opposite poles connected to said electrodes, an electronic amplifier having its grid connected di rectly to one of said electrodes, and a telephone receiver operatively associated with said amplifier.

' sound the currents thus amplified.

4. The combination with means for producing a beam of light fluctuating with a frequency corresponding to that of sound waves, of a photoelectric cell arranged in the path of said beam. said cell comprising an evacuated vessel having a cathode having on its interior a light 3. The combination with means for producing sensitive coating containing an alkali metal, conltituting one electrode, and provided with another electrode, a thermionic amplifier having its grid directly connected with one of said electrodes, a current source suitably connected with said amplifier and with the other electrode, and a telephone receiver operatlvely associated with said amplifier.

5. Means for converting a fluctuating beam of light into sound comprising a photo-electric cell on to which the beam is projected, said cell having a pair of electrodes, a battery, conductors connecting opposite poles of said battery with said electrodes, one of said conductors containing a relatively high ohmic resistance, a thermionic amplifier having its grid connected to said last mentioned conductor at a. point between said resistance and the cell electrode, and a telephone receiver operatively connected in the plate circuit ofsaid amplifier.

6. The electro-optical method of reproducing sound which comprises generating a beam of light which fluctuates in synchronism with the vibrations of the sound to be reproduced, causing such fluctuating beam to set up, in a suitable circuit, electric currents varying in absolute synchronism with said beam, thermionically amplifying such currents, and converting the energy of the amplified currents into sound waves.

'7. The combination with a photo-electric cell having two electrodes, and a current source connected with said electrodes, of means for amplifying feeble variations of current flowing from said battery through said cell comprising a purely ohmic resistance inserted in the circuit between the battery and one electrode, and a thermionic amplifier having its grid connected directly with said last mentioned electrode and its cathode with an intermediate point of said current source.

8. The combination with a photo-electric cell having two electrodes, and a current source connected with said electrodes, of means for amplifying feeble variations of current flowing from said current source through said cell comprising a fixed ohmic resistance of the same order of magnitude as that of said cell inserted in the circuit between the battery and one electrode, and a thermionic amplifier having its grid connected directly with said last mentioned electrode and its cathode with an intermediate point of said current source.

9. The method of effecting a photo-electric cell by means of a fluctuating beam of light, which comprises obscuring the central part of said beam, and exposing the cell only to that-part of the beam of a width in excess of such obscured portion.

10. The method of efi'ecting a photo-electric cell by means of a fluctuating beam of light which varies in width from a definite fixed minimum to an indefinite maximum, said method comprising shielding the cell from being acted on by the beam when at its minimum width, and exposing it only to that variable portion of the beam which exceeds such width.

11. The method of eflecting a photo-electric cell by means of a fluctuating beam of light 0! variable width, which comprises exposing the cell to'those portions only of the beam which exceed a definite minimum width.

12. The method of optically reproducing sound which comprises setting up a fluctuating beam of light which varies in accordance with the sound, and projecting this beam upon a photo-electric cell in such a way that the cell is continuously energized, whereby its conductivity never'drops to zero, but varies between maximum and a definite minimum.

13. A photo-electric cell comprising an evacuated vessel having its interior coated with light responsive material, and having an uncoated area constituting a window", the central portion of said window being opaque, with transparent portions at each side thereof.

14. A photo-electric cell comprising an evacuated vessel having its interior coated with light responsive material, and having an uncoated area constituting a window, and an opaque strip or shield extending centrally across said window.

15. The combination with means for generating a fluctuating beam of light which varies in width from an indefinite maximum to a definite minimum, of a photo-electric cell onto which said beam is projected, said cell comprising an evacuated vessel having its interior coated with light responsive material, and having a. transparent window through which the light enters, and a strip of opaque material of substantially the same width as the said minimum width of the beam extending across said window.

16. The combination with a record strip having a transparent record thereon, said record comprising a central band and teeth or projections extending from each edge thereof, of means for causing said record strip to travel, means for projecting the image of said transparent record as the strip travels past a slit, a photo-electric cell having a transparent window" on which said image is projected, and an opaque strip or shield of substantially the same width as the image of the central band portion of said record extending across the window and serving to prevent that portion of the image from entering the window and aflecting the cell.

1'7. The combination with a circuit having connected in series therein a photoelectric cell, a source of electromotive force and an ohmic resistance, of a thermionic amplifier having its grid connected to said circuit at a point between the ohmic resistance and the photoelectric cell, and having its cathode connected to a point of intermediate potential in said source of electromotive force.

18. Means for optically producing sound, including a. sheet or the like having relatively opaque and transparent portions, a source of light, a photo-electric cell comprising an evacuated vessel having a cathode having on its innersurface a light sensitive coating containing an alkali metal, said source of light being so arranged as to direct a beam upon said alkali metal coating, and said sheet being interposed between said source and said cell, means for rapidly moving said sheet so as to cause the relatively opaque and transparentportions thereof to successively pass across the path of said beam at a speed equal to the frequency of sound vibrations, a current source suitably connected in a circuit including said cell, whereby the fluctuating beam produced by said moving sheet sets up similarly varying currents of feeble intensity, 9, three-element vacuum tube arranged to amplify such feeble currents, and a device for converting into sound the currents thus amplified.

19. The electro-optical method of producing sound which comprises forming on a sheet or strip a series of lines or hands having optical properties in contrast with those of said sheet, directing a beam of light upon said sheet, moving said sheet in such manner as to cause said beam, after leaving the sheet, to fluctuate with a frequency equal to that of sound vibrations, causing such fluctuating beam to set up, in a suitable circuit, electric currents varying in absolute synchronism with said beam, thermionically amplifying such currents, and converting the energy of the amplified currents into sound waves.

20. Sound producing apparatus comprising a photoelectric cell having an anode and an alkali cathode, means for illuminating the cell and for varying such illumination at a rate corresponding to the frequency of sound waves, and a circuit connected with the electrodes of said cell and containing a source of electricity, in which circuit flows a correspondingly varying feeble current and an electronic amplifier external to but coupled to said circuit.

21. Sound producing apparatus comprising, in combination, a photoelectric cell having an anode and an alkali cathode, and capableof responding to light variations of a frequency equal to that-of sound waves, a source of light for illuminating said cell, a movable light-varying element interposed in the path of the light rays between said sourceand' said cell, a circuit connected with the electrodes of said cell and containing a source of current, an electronic amplifier external to but coupled with said circuit-and an electrical sound producing device associated with said amplifier and operated by current fluctuations corresponding with said light variations.

22. Sound producing apparatus comprising a photoelectric cell having an anode and an alkali cathode, means for illuminating the cell and for varying such illumination at a rate corresponding to the frequency of sound waves, an amplifier, a circuit connecting said cell with said amplifier, a sound producing device, and a circuit connecting said amplifier with said sound producing device.

23. Sound producing apparatus comprising, in combination, a photo-electric cell having an anode and an alkali cathode, a circuit connected with the electrodes of said cell and containing a source of current, an electrical sound producing device operatively associated with said circuit, a source of light for illuminating said cell, and means for causing the illumination of said cell to vary at a rate corresponding to the frequency ofsound waves, said means including a movable element interposed in the path of the light rays between said source and said cell.

24. Means in combination for transforming light impulses into electric current impulses com-' prising a cathode, agrid and a plate, a plate circuit including a source of current for the traverse of said electric current impulses; a photoelectric body adapted to be subjected to light impulses; an envelope for maintaining said body in a cooperative atmosphere; provisions tending toproduce and maintain a negative normal potential i'is for said body but themselves incapable of maintaining said potential when said body is being subjected to light; and a'link-means electrically connecting said body and said grid and adapted. to impart potential variations to said grid corresponding to those which take place on said body.

25. In combination, a photo-electric couple having an envelope to maintain it in a cooperative atmosphere and comprising a photo-electric cathode-body, adapted to be subjected to'lig'ht 1mpulses, and an anode; a cathode. a grid and a plate; a source of direct current and aileakage resistance connected in series with saidsphotoelectric couple, the negative terminal of said -source having a connection with said cathode and leading to said cathode-body and the positive terminal of said source leading to said anode; and a link-means electrically connecting said cathodebody and said grid and adapted to impart potential variations to said grid corresponding to those which take place on said body in response to said light impulses, whereby appreciable corresponding impulses in electron-flow to said plate are effected.

26. In combination a photo-electric couple in a cooperative atmosphere; a current-strength-controller operating by reason of changes in potential; a link-means electrically connecting one electrode of said photo-electric couple with said ourrent-strength controller and adapted to impart potential variations to said controller corresponding to those which take place on said electrode; and provisions tending to produce and maintain a negative normal potential for the cathode of said photo-electric couple, but said provisionsbeing body exposable to light variations and in a cooperative atmosphere; a grid which controls a current flow by reason of potential; and a linkmeans between said cathode-body and said grid to control the potential of said grid by potential changes in said cathode-body; and provisions in addition to said link-means tending to maintain a fixed charge on said cathode-body.

28. Means in combination for transforming light impulses into electric current impulses including an electron emitting cathode, a grid and a plate: a plate circuit including a source of direct current and forming the circuit for said current impulses; a photo-electric cathode-body; an anode for said photo-electric cathode-body; an electric connection between said photo-electric cathode-body and said grid of such character as to impart substantially instantaneously'a change of potential in said photo-electric cathode-body to said grid; provisions in addition to said electric connectlonbetween said photo-electric cathode body and said grid for negatively charging said photo-electric cathode-body; andprovisions for capable of substantially completely restoring the potential of said photo-electric body after elcetrons are emitted therefrom in response to light,

but incapable of maintaining the potential of said photo-electric body when it is being subjected to light; subjecting said photo-electric body to the action of a variable source of light-and thereby effecting corresponding potential changes in said photoectric body and imparting the controlling .eflect of -said potential changes in said photoelectric body to thestream of cathode'emitted free electrons of a plate circuit.

30. In sound reproducing apparatus, the come binationof a photoelectric cell having an alkali cathode, means for illuminating the cell with acoustically-modulated light, and a circuit including an electronic amplifier which amplifier is connected with said cell in which said circuit flows a correspondingly modulated current.

31. In sound reproducing apparatus, the combination of a photoelectric cell having an alkali cathode, a constant source of light, means for uniformly progressing a film between said source and cell, said film carrying a photographic sound record of varying opacity, so that said cell is illuminated by acoustically-modulated light, which has passed through the film, and a circuit including an amplifier coupled with said cell in which flows a correspondingly modulated current.

32. In sound reproducing apparatus, the combination of a photoelectric cell having an alkali cathode, means for illuminating the cell with acoustically-modulated light, an amplifier. a circuit connecting said cell with said amplifier, a sound reproducing device, and a circuit connecting said amplifier with said sound reproducing device.

33. In sound reproducing apparatus, the com bination of a photoelectric cell having an alkali cathode, means for illuminating the cell with acoustically-modulated light, an amplifier, a circuit connecting said cell with said amplifier, and a circuit connected with said amplifier, in which fiows amplified currents which vary correspondingly with the variations of said acoustically-modulated light.

34. In sound reproducing apparatus, the combination of a photoelectric cell having an alkali cathode; a source of light substantially constant relatively to variations within the audible range; means for uniformly progressing a record strip through the light field between said source of light and said cell; said strip carrying an optical sound record varying lengthwise of said strip.. so that said cell is illuminated by a oustically modulated light which has passed from said source to said strip and thence to said cell; and a circuit including an amplifier coupled with said cell in which flows a correspondingly modulated current.

35. In sound producing apparatus from an optical record, an electrically operated sound producer requiring modulated dynamic electrical energy of substantial value for its operation; a photoelectric cell having an anode and a cathode capable of emitting electrons in proportion to incident light and a protecting enclosure having a transparent portion adapted to expose said cathode to light modulated by an optical record; a source of electric exciter potential for said photoelectric cell: an amplifier operatively con-' nected with said sound producer; and means operatively connecting said source of exciter potential with said photoelectric cell and linking said photoelectric cell with said amplifier operatively to cause modulated electron emission from said cathode to eifect the fiow of correspondingly modulated but greatly amplified currents from said amplifier through said sound producer.

38. In sound reproducing apparatus, the combination of a photoelectric cell having an alkali cathode; means for illuminating said cell with acoustically modulated light; and a circuit including an electronic amplifier which amplifier is connected with said cell in which said circuit flows a correspondingly modulated direct current.

3'1. In sound reproducing apparatus, the combination of a photoelectric cell having an alkali -cathode; a source of light; means for uniformly progressing an optical record strip relatively to said source of light and said cell for modulating thelight reaching said cell from said source; said strip carrying an optical sound record varying lengthwise thereof, so that said cell is illuminated by acoustically modulated light, which has passed from said source to said strip and to said cell; and a circuit connected with said cell and including an electronic amplifier in which fiows a correspondingly modulated direct current.

38. In sound reproducing apparatus, the combination of a photoelectric cell having an alkali cathode, a constant source of light, means for uniformly progressing a film between said source and cell, said film carrying a photographic sound record of varying opacity, so that said cell is illuminated by acoustically modulated light, which has passed through said film, and a direct current amplifier circuit connected with said cell in which flows a correspondingly modulated direct current.

39. In sound producing apparatus from an optical record, an electrically operated sound producer requiring modulated dynamic electrical energy of substantial value for its operation; a

' photoelectric cell having an anode and a cathode capable of emitting electrons in proportion to incident light and a protecting enclosure having a transparent portion adapted to expose said cathode to light modulated by an optical record; a direct current source of electric exciter potential for said photoelectric cell; a vacuum tube amplifier operatively connected with said sound producer; and means operatively connecting said source of exciter potential with said photoelectric cell and linking said photoelectric cell with said amplifier operatively to cause modulated electron emission from said cathode to eflfect the flow of correspondingly modulated but greatly amplified currents from said amplifier through said sound producer- 40. In sound reproducing apparatus, the combination of a photoelectric cell having an alkali cathode; means for illuminating said cell with acoustically modulated light; an amplifier; a direct current circuit connecting said cell with said amplifier; a sound reproducing device; and a circuit connecting said amplifier with said sound reproducing device.

41. In sound reproducing apparatus, the combination of a photoelectric cell having an alkali cathode; means for iluminating said cell with acoustically modulated light; an amplifier; a direct current circuit connecting said cell with said amplifier; and a circuit connected with said amplifier, in which circuit flow amplified currents which vary correspondingly with the variations of said acoustically modulated light.

42. Apparatus operable over a substantial period of time for transforming small light impulses into substantially relatively proportional electric current impulses comprising cooperable electrodes of a photo-electric couple including a photo-electric cathode and its anode, both in a cooperative atmosphere; a thermionic amplifier having a grid, a cathode anda plate; a plate circuit for said relatively proportional current impulses; a restoration impedance of the order of magnitude'of the apparent impedance between the electrodes of said photo-electric couple when its said cathode is being subjected to said light impulses and said impedance being electrically connected between the cathode of said thermionic amplifier and one of said electrodes of said photo-electric couple; a link means free from any substantial capacity coupling or other itself linking said one of said electrodes of said photo-electric couple with the said grid of said thermionic amplifier; and a source of activating electricity connected to the other electrode of said photo-electric couple, to the cathode of said cooperative atmosphere; a thermionic amplifier having a grid, a cathode anda plate; a plate circuit for said relatively proportional current impulses; a restoration impedance of. the order of magnitude of the apparent impedance between' the electrodes of said photo-electric couple when its said cathode is being subjected to said light impulses and said impedance being electrically.

connected between the cathode of said thermionic amplifier and one of said electrodes'oi said photoelectric couple; a link means free from any substantial capacity coupling or other coupling except said restoration impedance with said cathode of said thermionic amplifier and itself linking said one of said electrodes of said photo-electric couple with the said grid of said thermionlc amplifier; a source of activating electricity connected to the other electrode of said photo-electric couple, to the cathode of said thermionic amplifier and through said restoration impedance to saidone of said electrodes of said photoelectric couple; and provisions for selectively biasing the average potential of said tively to its cathode.

45. Apparatus in combination for transforming light impulses into substantially corresponding appreciable current impulses over a substantial period of time including a photo-electric couple having cooperating electrodes in a cooperative atmosphere including an anode and a photoelectric cathode; an electronic amplifier having a grid, a cathode and a plate; a link means connecting one of the electrodes of said photo-electric couple directly with said grid; a restoration impedance. of the order of magnitude of the apparent impedance of said photo-electric couple .when subjected to said light impulses; .and asource of exciting potential forsaid photo-electric couple connected at one terminal to the cathode of said electronic amplifier and through said restoration impedance to said one of the electrodes of said photo-electric couple which is linked to said grid and at the other terminal to the other electrode of said photo-electric couple.

46. Apparatus in combination for transforming light impulses into substantially corresponding appreciable current impulses over a substantial period of time including a photo-electric conple having cooperating electrodes in a cooperative atmosphere including an anode and a photo-electric cathode;- an electronic amplifier having a grid, a cathode and a plate; a link means con-' necting one of the electrodes of said photo-electric couple with said grid; a-restoration impedance of the order of magnitude of the apparent impedance of said photo-electnc couple when grid rela coupling except said restoration impedance with' said'cathode of said thermionic amplifier and subjected to said light impulses; a source of excitin potential for said photo-electric couple connected at one terminal to the cathode of said electronic amplifier and through said restoration impedance to said one of the electrodes of said photo-electric couple which is linked to said grid and at the other terminal to the other electrode of said photo-electriccouple; and provisions for biasing said grid relatively to its cathode without destroying the control of its potential by said photo-electric couple.

47.-Means for transforming rapid light impulses into faithfully corresponding electrical impulses of practically usable magnitudes comprising a multi-electrode photo-electric device which has at'least an electron emitting alkali cathode and an electron collecting anode spaced from said-cathode in a rarefied cooperative atmosphere with provisions for maintaining said cooperative atmosphere, in combination with an electronic amplifier having a control electrode and an output circuit in which said corresponding electrical impulses of practically usable magnitude flow; a source of electric potential and link means for applying an appropriate activating potential directly to the electrodes of said photo electric device independently from electronic flow in said electronic amplifier and also for imparting the controlling effect of light responsive electronic flow in said photo-electric device to said control element of said electronic amplifier to effect the control of amplified current impulses in said output circuit of said electronic amplifier.

48. The combination for transforming rapid light variations faithfully into corresponding electrical variations of readily employable magnitude including a spaced-electrode photo-electric device having provisions for fixing and maintaining its electrodes in a cooperative atmosphere;

. an electronic amplifier having parts including a control grid, a cathode and an anode; a source of electrical excitation for said photo-electric device; means for completing a circuit from said source to the electrodes of .said photo-electric device independently of current flow in said electronic amplifier but including part of a variable potential link means between said photo-electric device and said electronic amplifier; potential means and connections for setting a negative bias for said control grid relatively to its cathode and for completing said variable potential link means to impart output controlling potential variations to said control grid in response to varying electron .emissions from said cathode otsa'id photo-electric device when exposed to said light variations; and meanszior completing an output circuit for said electronic amplifier-for .the flow oi electrical energy variation of readily employable magnitude and corresponding faithtully to said rapid light variations.

49. Electric reproducing apparatus for utilizing light variations corresponding in frequency and relative variation to sound vibrations, the combination of a photo-electric cell having plural electrodes including an alkali cathode and an anode; an electronic amplifier having an output circuit, for the flow of amplified current variations corresponding to said light variations} means ior illuminating said cathode of said photo-electric cell with said light variations: and

.means including a source of electric energy for activating-said photo-electric cell and for linking the effect of electron emissions from said cathode to control said electronic amplifier independently of electronic flow therein and maintain ng said link me'ans'substantially tree from capacity ecupling in shunt to said controlling efiect.

50. Means for transforming rapid light impulses into faithfully corresponding electrical impulses of practically usable magnitudes comprising, a. multi-electrode photo-electric device which has at least an electron emitting alkali cathode and an electron collecting anode spaced from said cathode in a rarefied cooperative atmosphere with provisions for maintaining said cooperative atmosphere, in combination with an electronic amplifier having an output circuit in which said corresponding electrical impulses or practically usable magnitude fiow; sources of electric potential and link means for applying appropriate activating potentials to the electrodes of said photo electric device and to said electronic amplifier and for linking without distortion the eflects oi the electron emissions from said alkali cathode to control the amplified current impulses of said electronic amplifier free and independently oi the fiowof electrons in said electronic amplifier in the activation of said photo-electric device.

51. In combination a plural electrode photoelectric device having a partially evacuated envelope enclosing an anode and a photo-electric cathode body; means for applying light pulsations to said cathode body; an electronic amplifying devic'e having anode, cathode and grid electrodes; a source of current and a high impedance connected in series with said photo-electric device; and a link means cooperating directly between one of the electrodes of said photo-electric device and the grid 01' said electronic amplifier to convey potential variationsof said' electrode to said grid for influencing an electron flow in said electronic amplifier to produce amplified current pulsations to said plate corresponding to the pulsations oi the said light.

52. The combination as characterized in claim 51 but further defined by the fact that said link means is in the form of a direct current conductive connection.

53. In combination a plural electrode photoelectric device having a partially evacuated envelope enclosing an anode and a photo-electric cathode body; means for applying light pulsations to said cathode body; an electronic amplifier device having anode, cathode and grid electrodes;

a source of current and a high impedance con-' nected in series with said photo-electric device; and a link means directly connected between said cathode body and the grid of the said electronic amplifier to convey potential variations oi said cathode body to said grid for influencing an electron flow in said electronic amplifier to pro-,

duce amplified current pulsations to said plate corresponding to the pulsations oi the said light. 60

electric device having a partially evacuated envelope enclosing an anode and a photo-electric cathode body; means for applying light pulsations to said cathode body; an electronic amplifier device having anode, cathode and grid electrodes; a source of direct current and a high resistance connected in series with said photo-electric device, the respective negative and positive terminals of said source being connected respectively to 70 said cathode body and said anode of said photoelectric device; and a direct current conductive connection directly connected between said cathode body and the grid of said electronic amplifier to convey potential variations of said '75 cathode body to said grid for influencing an elec-' 54. In combination a pluralelectrode photoamplified current pulsations to said plate corresponding to the pulsations oi the said light.

55. A photocell system comprising a photographic sound record means, a record track 5. thereon having a plurality of record traces regarding the same sound, a shield cooperating therewith and a photocell and amplifier system receiving light therefrom for the production of a usable value of pulsating current correspondl0 ing to the recorded sound,

58. Means in combination for transforming light impulses into electric current impulses comprising an' electron amplifier member having cathode grid and plate electrodes, a plate output circuit including a source of current; a photoelectric body, means for applying pulsating light thereto, an anode and envelope cooperating therewith, circuit members and a source of potential I tending to produce and maintain a relative nega- 2o tive potential on said photo-electric body but incapable of maintaining said potential when said body-is illuminated and a link means connected directly between said body and the grid of said electron amplifier member to impart potential variations occurring on said body to said grid to produce electric current pulsations in said plate output circuit. a

5'7. In combination, a photo-electric couple, a potential-operated current-strength-controller device, a link means directly electrically connecting an electrode'oi said photo-electric couple with said current-strength-controller for" conveying potential variations developed by said photo electric couple to said controller; and circuit members tending to produce and maintain a normal potential between the electrodes of said photo-electric couple but incapable of maintaining a full potential therebetweem when said photo-electric couple is illuminated with pulsat- 40 ing light rays but permitting said potential variations.

58. In combination, a photo-electric cathode body, means for producing a cooperative atmos- -phere threaround, a source. of pulsating light 5 rays applicable thereto, an electron amplifier device having a grid and a link means between said cathode body for directly conveying potential variations produced on said cathode body to said Grid and a resistive current supply circuit to said cathode body tending to maintain a fixed potential v on said body but incapable of .doing'so when said body is illuminated. I

59. In sound reproducing apparatus, the combination of a photoelectric cell having a photoelectric cathode, an anode, an evacuated envelope and an energizing means including a source of. current cooperating therewith, means, for illuminating the cell with acoustically modulated. light, a circuit connected with-said cell in which 0 "flows a current'modulated inaccordance with the modulations, of said light, an amplifier systemconnected to said circuit, and having an output circuit carrying an amplified current having modulations corresponding to the modulations of 55 between said light and said cell to impress acoustic modulations upon the lightreaching said cell, a circuit connected with said cell having a source 01' energizing power therein and carrying a modulated electric current corresponding to the modulations of said light rays produced by said sound record, an electronic amplifier system connected to said circuit having an output circuit in which there flows an amplified current having modulations corresponding to the modulations impressed upon said light rays by said record, and a translating means for converting the modulations of said output current into sound.

61. In sound reproducing apparatus, the combination of a photoelectric cell having a thermionic alkali cathode, an anode and an evacuated container, a constant source of light projecting light rays upon said cathode, a sound record comprising members for variably controlling the said light rays to provide an acoustically modulated light upon said cathode, means for traversing said sound record past said light rays at a substantially uniform rate of speed and a work circuit connected to said cell and carrying an electric current modulated in accordance with the said sound record.

ulated light upon said cathode, means for traversing said sound record past said light rays at a substantially uniform ratev of speed, a worlr circuit connected tosaid cell and carrying on electric current modulated in accordance with the said sound record, an electronic amplifier system having a grid, a cathode, and an anode, circuit members connecting said grid to said work circult, and an output circuit connected to said plate for carrying a current having amplified modulations corresponding to the said sound record.

63. In sound reproducing apparatus, the combination of a photoelectric cell having a therm-- i'onic alkali cathode, an anode and an evacuated container, a constant source of light projecting light rays upon the said cathode, a sound record comprising members for variably controlling the said light rays to provide an acoustically modulated light upon said cathode, means for traversing said sound record past said light rays at 'a substantially uniform rate 01 speed, a work circuit connected to said cell and carrying an electric current modulated in accordance with the said sound record, an electronic amplifier system having a grid, a cathode,'and an anode, circuit members connecting saidgrid to said workcircuit, an output circuit'connected to said plate for carrying a current having amplified modulations corresponding to the said'sound record and a translating device connected to said output circuit for converting the modulations of said output current into sound.

A 64. 'In sound reproducing apparasitus, the combination oi a photoelectric cell having an alkali cathode, an anode and an evacuated container, means for illuminating the said cell cathode with acoustically modulated light, an electronic amplifier having a cathode, an anode and/a control electrode, a circuit connecting said cell with the of said amplifier, a source-oi pcwer'for said circuit connected with the plate of said amplifier in which fiows amplified currents varying correspondingly with the variations of said acoustically modulated light.

65. In sound reproducing apparatus, the comwith acoustically modulated light, on electronic modifier means having a cathode, an anode and a control electrode, a circuit connecting said cell with the grid of said amplifier, a source or power for said cell also connected in said circuit, an output circuit connected with the plate of said amplifier in which flows amplified currents varying correspondingly with the variations of said acoustically modulated light and a translating device connected to said plate circuit for converting the amplified currents into sound.

66. The method of translating film sound records intoelectrical eii'ects varying substantially in accordance with the sounds originally recorded, which comprises controlling the light falling on a light sensitive cell in accordance with consecutive portions of the film sound record and in restrict ing the light so falling on said cell substantially to light variations corresponding to the sounds originally recorded. w V a 67. The process of reproducing sound, comprising impressing light from consecutive portions 01 a photographic record'upon a single light responsive device and corresponding to the originally recorded sound.- pulsaticns and simultaneously obscuring the lightfrom said record in excess of that corresponding to the original sounds. A

68. The. method or translating a photographic sound record of modulated light into electrical impulses varying in accordance with the sounds originally recorded, which comprises first substantially suppressing the unmodulated com'pomm of said modulated light record and later translating said sound record into electrical impulses which consist substantially wholly oi variations corresponding to the sounds originally recorded to the substantial exclusion of unmodu- ,lated efiects by impressing consecutive portions of said impulses upon the same light responsive device, thereby translating said impulses into sound, 69. In a sound translating system, the combination of a source of light, a photo cell, an optical a circuit associated with the; electrodes of said' cell and having an impedance substantially equal to the cell impedance. a

71. In a sound translating system-the combination 01' a source of light, a photo cell, an optical sound record strip therebetween, a vacuum tube.

device having a control electrode associated with said cell, and a current source and connections therefor wherebysald current source serves the double function or. polarizing said control elec-.

trode and said cell. I 72., The combination or a photo cell havingcathode and anode electrodes, a vacuum tube d'e- "l6 tioned sections and another section furnishes space current to said photo cell and one of said last mentioned sections furnishes a polarizing potential for said control electrode.

73. The method of aifecting a photo-electric cellbymeansof afiuctuating beamoflightwhich varies-in width from a definite fixed to an indefinite maximum, said method comprising shieldingasinglecelifrombeingactedonbythe beam when at its minimum width, and exposing said single cell only to the consecutive portions of the beam which exceed such width.

74. The method of affecting a single photo'- electric cell by means ofa fluctuating beam of light of variable width, which comprises exposing said single cell to all those portions only of the beam which exceed a definite minimum width.

'15. The method of optically reproducing sound which comprises setting up a fluctuating beam of light which varies in accordance with the sound, and projecting this beam upon a photo-electric I cell in such a way that the cell is continuously energized, whereby its conductivity never drops to zero, but varies between maximum and a definite 76. The combination with means for generating a fluctuating beam of light which varies in width from an indefinite maximum to a definite minimum, of a photo-electric cellonto which said beam is projected, said cell comprising an evacuated vessel having its interior coated with light responsive material, and having a transparent window through which the light enters, and a strip of opaque materialof substantially the same width as the'said minimum width of the beam extending across said window.

7'7. The combination with a record strip having a transparent record thereon, said record comprising a central band and teeth or projections extending from eachedge thereof, of means for causing said record strip to travel, means for projecting the image of said transparent record as the strip travels past a slit, a photo-electric cell having a transparent "window on which said image is projected, and an opaque strip orshield of substantially the same width as the image of the central band portion of said record extending across the window and serving to prevent that portion of the image from entering the window and affecting the cell.

78. The combination with means for producins a beam of light fluctuating with a frequency corresponding to that of sound waves, of a photoelectric cell comprising an.evacuated vessel having on its inner surface a light sensitive coating containing an alkali metal, said cell being so arranged that the fluctuating beam falls upon said alkali metal coating, a potential source suitahly connected in a circuit including said cell.

whereby said fluctuating beam sets up variable currents of feeble intensity, a three-element vacuum tube arranged to amplify such feeble cur rents, and a device for converting into soundthe currents thus'amplified. I

'79. The combination with means for producing a beam of light fluctuating with a frequency corresponding to that of sound of a photoelectric cell arranged in the path of said beam,

said cell comprising an evacuated vessel having sensitive coating containing an alkali metal, said on its interior-surface alight sensitive costing containing an alkali metal, constituting one electrode, and-provided with another electro'de,'a thermionic amplifier having its grid directly connected with one'of said electrodes, a potential source suitably connected with said amplifier and with the other electrode, and a telephone receiver operatively associated with said amplifier.

80. Means for optically producing sound, including a sheet or thelike having relatively opaque and transparent portiona'a source of light, a photo-electric cell comprising an evacuated vessel having on its inner surface a light sourceoflightbeingsoarrangedastodirecta upon said alkalimetalcoatingand said sheet being interposed'between said source and said cell. means for rapidly moving said sheet so as to cause the relatively opaque and transparent portions thereof to successively pass across the so pathofsaidbeamataspeedequaltothefre-' quency of sound vibrations, a potential source suitable connected in a circuit including said cell. whereby the fluctuating beamproduce'd by said moving sheet .sets up similarly varying currents of feeble intensity. a three-element vacuum tube arranged to amplify such feeble currents, and a device for converting into sound the currents thus amplified.

81. The electro-optical method of producing sound which comprises forming on a sheet or strip a series of lines or hands having optical properties in contrast with those of said sheet, directing a beam of light upon said sheet, moving saidsheet in such manner as to cause said beam, after leaving the sheet, to fluctuate with a frequency equal to-that of sound vibrations; causing such fluctuating beam to set up, in a suitable circuit, electric currents varying in absolute synchronism with said beam, thermionically amplifying such currents. and converting the energy of the amplified currents into sound v waves.

82. Sound producing apparatus comprising a photoelectric cell having an anode and an alkali cathode, means for illuminating the cell and for varying such illumination at a rate corresponding to the frequency of sound waves, an amplifier, a circuit connecting said cell with said amplifier, a sound producing device, and a circuit connecting said amplifier with said sound producing device.

'83. In sound producing apparatus from an optical record, an electrically operated sound pro-' ducer requiring modulated dynamic electrical energy of substantial value for its operation; a photo-electric cell having an anode and a oath-- ode capable of emitting electrons in proportion to incident light and a protecting enclosure having a transparent portion adapted to expose said cathode to light modulated by an optical record; a direct current source of electric exciter potential for said photo-electric cell; a vacuum tube amplifier operatively connected with said-sound producer; and means operatively connecting s'ald source of exciter potential with said photoelectric cell and linking said photoelectric cell with said amplifier operatively tolcausemodulated electron emission from said cathode to effect the flow of correspondingly modulated but greatly amplified 7o currents from said amplifier through said sound producer; ALBERT A.

'CERTIFIGAIE OF CORRECTION.

Patent No. 2411 9 9. April 19, 19

ALBERT A. mum.

Since it appears from th'e'records of this Office that claims 2h, 25, 26, 2'; and 28 were held unpatentable to the patentee by the Board of Appeals and that claims 75, 7 6,* T7, 81, 82 and 85 are duplicatee' respectively of claims 12, l5, l6, 19, 22 and 59 of the patent, it is hereby certified that;

claims 2 25, 26, 27, 28, 75, T6, 77, 81, 82 and 85 were included in the patent by error and that-the patent should be reachwithout these claims.

Signed and sealed this 1st day of November, A. D. 1958 Henry Van A rsdale (Seal) Acting Commissioner of Patent 5. 

